Identification of provenance on uranium-bearing rocks from the Zhiluo Formation in the Nanlinggou uranium deposit, northern Ordos Basin

This paper is the result of mineral exploration engineering.

Objective The Nalinggou uranium deposit is one of the most important uranium deposits in northern Ordos Basin. Identification onthe provenance of uranium bearing rocks is of practical significance for deepening mineralization and prospecting prediction.

Methods By means of petrology, heavy mineralogy, geochemistry and sedimentary facies analysis, the authors have identified the provenance of the uranium bearing rocks from the Middle Jurassic Zhiluo Formation in the Nalinggou uranium deposit.

Results The uranium-bearing rocks are dominantly composed of medium coarse arkose. The clastic components are feldspar, quartz, biotite, debrises of granite and metamorphic rock, etc., with medium to poor sorting. The clasts are mostly angular and sub-angular, and a few are sub-rounded, with poor to medium roundness. The distribution of heavy minerals is extremely uneven, in angular, sub angular and sub rounded shapes, with poor to medium roundness. The ZTR (zircon+tourmaline+rutile) index varies of 2%-10%. The tourmaline, spinel, anatase, amphibole and carbosilica are distributed in clusters.The extension coefficient of detrital zircon is mainly in the range of 1-2.2, followed by the range of 2.2-3.2. The rocks exhibit similar chondrite-normalized patterns with great elemental variations among different samples. The ΣREE, LREE/HREE, and La/Yb values are in the range of 104.75×10^-6-283.86×10^-6, 0.13-0.47, and 9.60-32.66 respectively. The uranium bearing strata exhibit highly thick sand bodies. In the mining area, the sedimentary facies extend synchronously from the northeast to the southwest.

Conclusions In conclusion, it is generally considered that the uranium bearing rocks of the Zhiluo Formation in the Nalinggou uranium deposit is mainly proximal provenance, with a small amount of distal provenance. The sourced rocks are the pre-Jurassic bedrock area exposed at the boundary between Shaanxi and Inner Mongolia on the northeast edge of the mining area. The rock types include Archean gneiss, Paleoproterozoic Khondalite, magmatic rocks, Paleozoic magmatic rocks, sedimentary rocks and Mesozoic volcanic rocks, of which the khondalite belt provides the most important materials.